1. Field of the Invention
This invention pertains to an optical memory device that uses a lens drive mechanism equipped with drive coils and magnetic circuits composed of magnets, etc., in order to drive an objective lens.
2. Description of the Related Art
Previously, well-known forms of magneto-optical memory devices have existed in which a magneto-optical disk equipped with a perpendicular magneto-optical recording film is used as a recording medium. These types of magneto-optical memory devices contain a magneto-optical disk that is rotated by a disk rotation drive mechanism, and the main surface of one side of this disk is equipped with electromagnets that are installed in an opposing fashion for the purpose of applying a bias magnetic field. The main surface of the other side of this disk is equipped with, optical pickup devices, also installed in an opposing fashion, for the purpose of irradiating a light beam.
In order for a writing process to be conducted onto the recording film of this magneto-optical memory device, a light beam strength is raised to an erasure power level, and an erasure field is applied to the magneto-optical disk in the erasure direction (which is nearly perpendicular to the medium and nearly parallel to the optical axis), such that an erasing operation is conducted over the specified area. Then, while the optical beam is modulated in response to the recording data signal that is supposed to be at the recording power level, a recording field, which has a reverse orientation with respect to the erasure field, is applied to the aforementioned specified area. This causes various shifts to occur in the magnetization direction of the magneto-optical disk, resulting in the recording of the data signals onto the aforementioned specified area.
In recent years, 3.5-inch magneto-optical disks have been able to achieve a storage capacity of 2.3 GB. And along with this move toward higher density, there has been a need for smaller recording marks as well as the formation of recording pits. For this reason, there has been a move toward smaller laser beam diameters as well as high numerical aperture (“NA”), resulting in the need for a closer distance between the optical memory medium and the objective lens. The closer distance, however, has resulted in problems due to magnetic effect on the optical memory medium as a result of magnetic flux leakage from the objective lens driver.
Furthermore, a sudden drop in costs, reduction in the number of parts, and greater demand for high-speed access have led to a need for simpler and smaller designs in the lens drivers used to drive objective lenses, as well as the carriage drivers that are used to move the lens drivers in specified directions of the optical memory medium.
Also, in the case of optical memory devices in which a power source is delivered from a host device through an interface, the amount of power that can be delivered is restricted according to the type of interface used, thus increasing the demand for a shift toward lower power consumption.
Accordingly, the objective of this invention is to provide an objective lens driver and an optical memory device that are designed with improved magnetic circuit constructions for the focusing and tracking operations of the objective lens driver, and in such a way as to reduce the level of power consumption.